It has been known to provide an apparatus of this type with several shafts arranged vertically in ring fashion in a common housing, with parallel axes and driven in equal direction. Each shaft carries a number of disk-shaped processing elements arranged axially in a row located in parallel planes, meshing with adjacent elements on adjacent shafts, forming narrow clearances of predetermined width and enclosing together with the shafts at least one cavity. A negative pressure is applied to the cavity. The processing elements are arranged in such a manner that their circumferential surfaces are exposed to the cavity. The shafts, which are rotatably mounted inside the housing, are formed with arrangements for the intake and discharge of material at their ends.
One such apparatus for the continuous production of longchain polymers is known from German Patent No. 30 30 541 by the applicant of this application, where the shafts carrying the disk-shaped processing elements are partly arranged in tub-shaped recesses of the housing wall which is formed by a rosette-shaped housing liner in whose tub-shaped recesses the processing elements of each shaft mesh with very narrow play. Into the space between the housing liner and the processing elements, flowable material fed into the apparatus is continuously conveyed in the form of thin layers through the narrow gaps between the meshing processing elements into the cavity that is connected to a source of negative pressure. Thus the material is being thoroughly mixed and kneaded while on the other hand it is presented due to the negative pressure in the cavity only in the form of defined thin layers which are continuously renewed. With progressive polymerization the negative pressure helps to remove the residual gas.
Many monomer mixtures are brought to polymerization temperature prior to polymerization while under pressure, being simultaneously mixed, for example in static mixers. This applies for example to the polycondensation of polyester.
When this heated mixture is conveyed by means of heated metering pumps into a reaction chamber, the mixture is expanded which leads to the formation of a voluminous foam. Since the known apparatus has no vacant spaces between the tub-shaped recesses of the rosette-shaped housing liner and the shafts or between the recesses and the partly surrounded processing elements, where the foam could expand, the known apparatus cannot be used for the processing of such materials.
Since the processed material is locally subjected to a very high degree of shearing stress--an undesirable feature for sensitive materials--in the area of the narrow gap between the outer circumferential surfaces of the processing elements and the adjacent wall of the tub-shaped recesses surrounding the processing elements on the side opposite the cavity, it has been suggested (in German Patent Disclosure Document DE-OS No. 34 30 885, to which PCT application No. 85/00283, now U.S. application Ser. No. 871,422, filed Mar. 31, 1986, by the inventor of this application, corresponds) to arrange the apparatus in such a way that over at least part of the length of the shafts the circumferential surfaces of the processing elements are exposed also on the outer side facing away from the cavity.
While this provides sufficient space for accommodating the voluminous foam between the inner wall of the housing liner and the processing elements and shafts, this foam has a tendency to adhere very tightly to the housing liner as well as to the processing elements. This means that the material to be processed would quickly burn on or sinter to the heated inner wall of the housing liner and thus contaminate the end product.